Some php color helper functions fork from avia framework by Christian "Kriesi" Budschedl

functions-color-helper.php

if(!function_exists('avia_backend_get_hex_from_rgb'))
{
	/**
	 *  converts an rgb string into a hex value and returns the string
	 *  @param string $r red
	 *  @param string $g green
	 *  @param string $B blue
	 *  @return string returns the converted string
	 */
 	function avia_backend_get_hex_from_rgb($r=FALSE, $g=FALSE, $b=FALSE) {
		$x = 255;
		$y = 0;
		
		$r = (is_int($r) && $r >= $y && $r <= $x) ? $r : 0;
		$g = (is_int($g) && $g >= $y && $g <= $x) ? $g : 0;
		$b = (is_int($b) && $b >= $y && $b <= $x) ? $b : 0;
		
		
		return sprintf('#%02X%02X%02X', $r, $g, $b);
	}
}


if(!function_exists('avia_backend_calculate_similar_color'))
{
	/**
	 *  calculates a darker or lighter color variation of a color
	 *  @param string $color hex color code
	 *  @param string $shade darker or lighter
	 *  @param int $amount how much darker or lighter
	 *  @return string returns the converted string
	 */
 	function avia_backend_calculate_similar_color($color, $shade, $amount) 
 	{
 	
 		//remove # from the begiining if available and make sure that it gets appended again at the end if it was found
 		$newcolor = "";
 		$prepend = "";
 		if(strpos($color,'#') !== false) 
 		{ 
 			$prepend = "#";
 			$color = substr($color, 1, strlen($color)); 
 		}
 		
 		//iterate over each character and increment or decrement it based on the passed settings
 		$nr = 0;
		while (isset($color[$nr])) 
		{
			$char = strtolower($color[$nr]);
			
			for($i = $amount; $i > 0; $i--)
			{
				if($shade == 'lighter')
				{
					switch($char)
					{
						case 9: $char = 'a'; break;
						case 'f': $char = 'f'; break;
						default: $char++;
					}
				}
				else if($shade == 'darker')
				{
					switch($char)
					{
						case 'a': $char = '9'; break;
						case '0': $char = '0'; break;
						default: $char = chr(ord($char) - 1 );
					}
				}
			}
			$nr ++;
			$newcolor.= $char;
		}
 		
		$newcolor = $prepend.$newcolor;
		return $newcolor;
	}
}

if(!function_exists('avia_backend_hex_to_rgb_array'))
{
	/**
	 *  converts an hex string into an rgb array
	 *  @param string $color hex color code
	 *  @return array $color 
	 */
	function avia_backend_hex_to_rgb_array($color) 
	{
		if(strpos($color,'#') !== false) 
		{ 
			$color = substr($color, 1, strlen($color)); 
		}
		
		$color = str_split($color, 2);
		foreach($color as $key => $c) $color[$key] = hexdec($c);
		
		return $color;
	}
}

if(!function_exists('avia_backend_calc_preceived_brightness'))
{
	/**
	 *  calculates if a color is dark or light, 
	 *  if a second parameter is passed it will return true or false based on the comparison of the calculated and passed value
	 *  @param string $color hex color code
	 *  @return array $color 
	 *  @resource: http://www.nbdtech.com/Blog/archive/2008/04/27/Calculating-the-Perceived-Brightness-of-a-Color.aspx
	 */
	function avia_backend_calc_preceived_brightness($color, $compare = false) 
	{
		$rgba = avia_backend_hex_to_rgb_array($color);
	
		$brighntess = sqrt(
	      $rgba[0] * $rgba[0] * 0.241 + 
	      $rgba[1] * $rgba[1] * 0.691 + 
	      $rgba[2] * $rgba[2] * 0.068);
		
		if($compare)
		{
			$brighntess = $brighntess < $compare ? true : false;
		}

		return $brighntess;
	}
}



if(!function_exists('avia_backend_merge_colors'))
{
	/**
	 *  merges to colors
	 *  @param string $color1 hex color code
	 *  @param string $color2 hex color code
	 *  @return new color 
	 */
	function avia_backend_merge_colors($color1, $color2) 
	{
		if(empty($color1)) return $color2;
		if(empty($color2)) return $color1;
	
		$prepend = array("", "");
		$colors  = array(avia_backend_hex_to_rgb_array($color1), avia_backend_hex_to_rgb_array($color2));
		
		$final = array();
		foreach($colors[0] as $key => $color)
		{
			$final[$key] = (int) ceil(($colors[0][$key] + $colors[1][$key]) / 2);
		}
	
		return avia_backend_get_hex_from_rgb($final[0], $final[1], $final[2]);
	
	}
}


function avia_backend_counter_color($color) 
{
	$color = avia_backend_hex_to_rgb_array($color);
	
	foreach($color as $key => $value)
	{
		$color[$key] = (int) (255 - $value);
	}
	
	return avia_backend_get_hex_from_rgb($color[0], $color[1], $color[2]); 
}